Semiconductor device and method for fabricating the same

ABSTRACT

A method for fabricating a semiconductor device includes the steps of: forming a first inter-metal dielectric (IMD) layer on a substrate; forming a first patterned mask on the first IMD layer, in which the first patterned mask includes a first slot extending along a first direction; forming a second patterned mask on the first patterned mask, in which the second patterned mask includes a second slot extending along a second direction and the first slot intersects the second slot to form a third slot; and forming a first metal interconnection in the third slot.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The invention relates to a semiconductor device and method forfabricating the same, and more particularly to a magnetoresistive randomaccess memory (MRAM) and method for fabricating the same.

2. Description of the Prior Art

Magnetoresistance (MR) effect has been known as a kind of effect causedby altering the resistance of a material through variation of outsidemagnetic field. The physical definition of such effect is defined as avariation in resistance obtained by dividing a difference in resistanceunder no magnetic interference by the original resistance. Currently, MReffect has been successfully utilized in production of hard disksthereby having important commercial values. Moreover, thecharacterization of utilizing GMR materials to generate differentresistance under different magnetized states could also be used tofabricate MRAM devices, which typically has the advantage of keepingstored data even when the device is not connected to an electricalsource.

The aforementioned MR effect has also been used in magnetic field sensorareas including but not limited to for example electronic compasscomponents used in global positioning system (GPS) of cellular phonesfor providing information regarding moving location to users. Currently,various magnetic field sensor technologies such as anisotropicmagnetoresistance (AMR) sensors, GMR sensors, magnetic tunnelingjunction (MTJ) sensors have been widely developed in the market.Nevertheless, most of these products still pose numerous shortcomingssuch as high chip area, high cost, high power consumption, limitedsensibility, and easily affected by temperature variation and how tocome up with an improved device to resolve these issues has become animportant task in this field.

SUMMARY OF THE INVENTION

According to an embodiment of the present invention, a method forfabricating a semiconductor device includes the steps of: forming afirst inter-metal dielectric (IMD) layer on a substrate; forming a firstpatterned mask on the first IMD layer, in which the first patterned maskincludes a first slot extending along a first direction; forming asecond patterned mask on the first patterned mask, in which the secondpatterned mask includes a second slot extending along a second directionand the first slot intersects the second slot to form a third slot; andforming a first metal interconnection in the third slot.

According to another aspect of the present invention, a semiconductordevice includes a metal interconnection on a substrate, in which a topview of the metal interconnection comprises a quadrilateral; and amagnetic tunneling junction (MTJ) on the metal interconnection, in whicha top view of the MTJ comprises a circular shape.

These and other objectives of the present invention will no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment that isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a method for fabricating a MRAM device according toan embodiment of the present invention.

FIGS. 2-5 illustrate a method for fabricating the MRAM device along thesectional line AA′ in FIG. 1 according to an embodiment of the presentinvention.

FIG. 6 illustrates a top view of the MTJ overlapping the metalinterconnection in FIG. 5 according to an embodiment of the presentinvention.

FIG. 7 illustrates a top view of the MTJ overlapping the metalinterconnection in FIG. 5 according to an embodiment of the presentinvention.

FIG. 8 illustrates a top view of the MTJ overlapping the metalinterconnection in FIG. 5 according to an embodiment of the presentinvention.

DETAILED DESCRIPTION

Referring to FIGS. 1-5 , FIG. 1 illustrates a method for fabricating asemiconductor device, or more specifically a MRAM device according to anembodiment of the present invention and FIGS. 2-5 illustrate a methodfor fabricating the MRAM device along the sectional line AA′ in FIG. 1according to an embodiment of the present invention. As shown in FIGS.1-2 , a substrate 12 made of semiconductor material is first provided,in which the semiconductor material could be selected from the groupconsisting of silicon (Si), germanium (Ge), Si—Ge compounds, siliconcarbide (SiC), and gallium arsenide (GaAs), and a MTJ region 14 and alogic region (not shown) are defined on the substrate 12.

Active devices such as metal-oxide semiconductor (MOS) transistors,passive devices, conductive layers, and interlayer dielectric (ILD)layer 16 could also be formed on top of the substrate 12. Morespecifically, planar MOS transistors or non-planar (such as FinFETs) MOStransistors could be formed on the substrate 12, in which the MOStransistors could include transistor elements such as gate structures(for example metal gates) and source/drain region, spacer, epitaxiallayer, and contact etch stop layer (CESL). The ILD layer 16 could beformed on the substrate 12 to cover the MOS transistors, and a pluralityof contact plugs could be formed in the ILD layer 16 to electricallyconnect to the gate structure and/or source/drain region of MOStransistors. Since the fabrication of planar or non-planar transistorsand ILD layer is well known to those skilled in the art, the details ofwhich are not explained herein for the sake of brevity.

Next, a metal interconnect structure 18 is formed on the ILD layer 16 toelectrically connect the aforementioned contact plugs, in which themetal interconnect structure 18 includes an inter-metal dielectric (IMD)layer 20, a selective stop layer (not shown), and metal interconnections22 embedded in the IMD layer 20. In this embodiment, each of the metalinterconnections 22 from the metal interconnect structure 18 preferablyincludes a trench conductor and each of the metal interconnections 22could be embedded within the IMD layer 20 and/or stop layer according toa single damascene process or dual damascene process. For instance, eachof the metal interconnections 22 could further include a barrier layerand a metal layer, in which the barrier layer could be selected from thegroup consisting of titanium (Ti), titanium nitride (TiN), tantalum(Ta), and tantalum nitride (TaN) and the metal layer could be selectedfrom the group consisting of tungsten (W), copper (Cu), aluminum (Al),titanium aluminide (TiAl), and cobalt tungsten phosphide (CoWP). Sincesingle damascene process and dual damascene process are well known tothose skilled in the art, the details of which are not explained hereinfor the sake of brevity. In this embodiment, the metal layers in themetal interconnections 22 are preferably made of copper, the IMD layers20 is preferably made of silicon oxide or ultra low-k (ULK) dielectriclayer, and the stop layer could be made of nitrogen doped carbide (NDC),silicon nitride, silicon carbon nitride (SiCN), or combination thereof.

Next, an IMD layer 24 is formed on the IMD layer 20 and the metalinterconnections 22, a first patterned mask 26 is formed on the IMDlayer 24, and then a second patterned mask 28 is formed on the firstpatterned mask 26. In this embodiment, the first patterned mask 26preferably includes a metal mask which could include titanium (Ti)and/or titanium nitride (TiN) while the second patterned mask 28preferably includes a patterned resist.

It should be noted that the first patterned mask 26 is preferably madeof a plurality of rectangular patterns extending along a first directionsuch as X-direction in FIG. 1 and the plurality of rectangular patternsof the first patterned mask 26 include a plurality of first openings orslots 30 therebetween also extending along the same first direction orX-direction, in which the edges of the first slots 30 are preferablyaligned with the edges of the metal interconnections 22 embedded in theIMD layer 20 underneath. The second patterned mask 28 on the other handis made of a plurality of rectangular patterns extending along a seconddirection such as Y-direction in FIG. 1 and the plurality of rectangularpatterns of the second patterned mask 28 includes a plurality of secondslots 32 therebetween, in which the second slots 32 are also extendingalong the same second direction such as Y-direction and intersecting thefirst slots 30.

Viewing from an overall perspective, portions constituted by rectangulardot lines extending along the X-direction in FIG. 1 are preferably thefirst patterned mask 26 while the portions also constituted byrectangular dot lines extending along the Y-direction are the secondslots 32 of the second patterned mask 28. It should be noted that therectangular first slots 30 and rectangular second slots 32 preferablyintersect each other and the intersecting portions of the first slots 30and second slots 32 preferably form a plurality of square third slots34, in which each of the third slots 34 defines the position of anothermetal interconnect used for connecting the metal interconnection 22 andthe edges of the third slots 34 are aligned with the edges of the metalinterconnections 22 underneath.

Next, as shown in FIG. 3 , an etching process is conducted by using thefirst patterned mask 26 and the second patterned mask 28 as a mask atthe same time to remove the IMD layer 24 within the third slots 34 forforming contact holes 36 exposing the metal interconnections 22underneath. Since the contact holes 36 are essentially extensions of thethird slots 34, the edges of the contact holes 36 are also aligned withthe edges of the metal interconnections 22 underneath.

Next, as shown in FIG. 4 , the second patterned mask 28 made of resistmaterial is removed and conductive materials are deposited into thecontact holes 36 thereafter. For instance, a barrier layer selected fromthe group consisting of titanium (Ti), titanium nitride (TiN), tantalum(Ta), and tantalum nitride (TaN) and metal layer selected from the groupconsisting of tungsten (W), copper (Cu), aluminum (Al), titaniumaluminide (TiAl), and cobalt tungsten phosphide (CoWP) could bedeposited into the contact holes 36, and a planarizing process such as(chemical mechanical polishing, CMP) could be conducted to remove partof the conductive materials including the aforementioned barrier layerand metal layer to form a contact plugs or metal interconnections 38 inthe contact holes 36 electrically connecting the metal interconnection22.

Next, as shown in FIG. 5 , a MTJ stack (not shown) or stack structure isformed on the metal interconnections 38 and IMD layer 24. In thisembodiment, the formation of the MTJ stack could be accomplished bysequentially forming a bottom electrode 42, a pinned layer 44, a barrierlayer 46, a free layer 48, and a top electrode 50. In this embodiment,the bottom electrode 42 and the top electrode 50 are made of conductivematerials including but not limited to for example tantalum (Ta),platinum (Pt), copper (Cu), gold (Au), aluminum (Al), or combinationthereof. The pinned layer 44 could be made of ferromagnetic materialincluding but not limited to for example iron, cobalt, nickel, or alloysthereof such as cobalt-iron-boron (CoFeB) or cobalt-iron (CoFe), inwhich the pinned layer 44 is formed to fix or limit the direction ofmagnetic moment of adjacent layers. The barrier layer 46 could be madeof insulating material including but not limited to for example oxidessuch as aluminum oxide (AlO_(x)) or magnesium oxide (MgO). The freelayer 48 could be made of ferromagnetic material including but notlimited to for example iron, cobalt, nickel, or alloys thereof such ascobalt-iron-boron (CoFeB) or nickel-iron (NiFe), in which the magnetizeddirection of the free layer 48 could be altered freely depending on theinfluence of outside magnetic field.

Next, one or more etching process is conducted by using a patterned hardmask 110 as mask (not shown) to remove part of the MTJ stack for formingMTJs 52 on the metal interconnections 38, in which the bottom electrodes42 are disposed under the MTJs 52 and top electrodes 50 are disposed ontop of the MTJs 52. It should be noted that a reactive ion etching (ME)process and/or an ion beam etching (IBE) process could be conducted topattern the MTJ stack and due to the characteristics of the IBE process,the top surface of the remaining IMD layer 24 could be slightly lowerthan the top surface of the metal interconnections 38 after the IBEprocess and the top surface of the IMD layer 24 also reveals a curve oran arc.

Next, a cap layer 56 is formed on the MTJs 52 and covering the surfaceof the IMD layer 24, an IMD layer 58 is formed on the cap layer 56, andone or more photo-etching process is conducted to remove part of the IMDlayer 58 and part of the cap layer 56 to form contact holes (not shown)exposing the top electrodes 50. Next, conductive materials are depositedinto the contact holes and planarizing process such as CMP is conductedto form metal interconnections 60 connecting the top electrodes 50underneath. Next, another stop layer 62 is formed on the IMD layer 58and covering the metal interconnections 60.

In this embodiment, the cap layer 56 preferably includes siliconnitride, but could also include other dielectric material including butnot limited to for example silicon oxide, silicon oxynitride (SiON), orSiCN depending on the demand of the product. The stop layer 62 couldinclude nitrogen doped carbide (NDC), silicon nitride, silicon carbonnitride (SiCN), and most preferably SiCN. Similar to the aforementionedmetal interconnections, the metal interconnections 60 could be formed inthe IMD layer 58 according to a single damascene process or dualdamascene process. For instance, each of the metal interconnection 60could further include a barrier layer and a metal layer, in which thebarrier layer could be selected from the group consisting of titanium(Ti), titanium nitride (TiN), tantalum (Ta), and tantalum nitride (TaN)and the metal layer could be selected from the group consisting oftungsten (W), copper (Cu), aluminum (Al), titanium aluminide (TiAl), andcobalt tungsten phosphide (CoWP). This completes the fabrication of asemiconductor device according to an embodiment of the presentinvention.

Referring to FIGS. 6-8 , FIGS. 6-8 illustrate top views of the MTJ 52overlapping the metal interconnection 38 in FIG. 5 according todifferent embodiments of the present invention. As shown in FIGS. 6-7 ,the metal interconnection 38 made of tungsten is disposed on the MRAMregion 14 while the MTJ 52 is dispose directly on top of the metalinterconnection 38 and the bottom electrode 42 directly under the MTJ 52contacts the metal interconnection 38 directly. Preferably, the metalinterconnection 38 if viewed from a top view perspective includes aquadrilateral, a square, or a rectangular shape while the MTJ 52includes a circular shape overlapping the square or rectangular shape ofthe metal interconnection 38 without contacting or passing over theedges of the square or rectangular shape.

Since the metal interconnection 38 is fabricated through the openingintersected by two patterned masks, the exterior profile or shape of themetal interconnection 38 could include a square shown in FIG. 6 or arectangle shown in FIG. 7 . On the other hand, the MTJ 52 is formed byan IBE process, the shape of the MTJ 52 preferably includes a circleshown in FIG. 6 or an ellipse shown in FIG. 7 . It should be noted thateven though the embodiment shown in FIG. 6 pertains to the combinationof a square metal interconnection 38 pairing a circular MTJ 52 while theembodiment shown in FIG. 7 pertains to the combination of a rectangularmetal interconnection 38 pairing an elliptical MTJ 52, according toother embodiments of the present invention it would also be desirable tointerchange the shapes of the metal interconnection 38 and MTJ 52 forforming different combinations of the elements. For instance, it wouldbe desirable to pair a square metal interconnection 38 with anelliptical MTJ 52 or a rectangular metal interconnection 38 with acircular MTJ 52 depending on the demand of the product, which are allwithin the scope of the present invention.

Next, as shown in FIG. 8 , in contrast the MTJs 52 in FIGS. 6-7 are alldisposed within the boundary of the metal interconnection 38 withoutoverlapping or exceeding the boundary of the metal interconnection 38,it would also be desirable to adjust the size of MTJ 52 or shift theposition of the MTJ 52 by overlapping at least an edge such as one side,two sides, three sides, or even four sides of the metal interconnection38 with the MTJ 52, which are all within the scope of the presentinvention.

Overall, the present invention first forms an IMD layer on the substrateand then forms a first patterned mask on the IMD layer as the firstpatterned mask includes a first slot extending along a first direction.Next, a second patterned mask is formed on the first patterned mask, inwhich the second patterned mask includes a second slot extending along asecond direction and the first slot intersects the second slot to form athird slot. Next a metal interconnection is formed in the third slot anda MTJ is formed on the metal interconnection thereafter. By using theaforementioned dual patterned mask to form a MRAM device it would bedesirable to fabricate metal interconnection with much smaller pitch asprocess window and size of the memory device decreases.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device and method may be made whileretaining the teachings of the invention. Accordingly, the abovedisclosure should be construed as limited only by the metes and boundsof the appended claims.

What is claimed is:
 1. A method for fabricating a semiconductor device,comprising: forming a first inter-metal dielectric (IMD) layer on asubstrate; forming a first metal interconnection in the first IMD layer;forming a second IMD layer on the first IMD layer and the first metalinterconnection; forming a first patterned mask on the second IMD layer,wherein the first patterned mask comprises a first slot extending alonga first direction and overlapping the first metal interconnection;forming a second patterned mask on the first patterned mask, wherein thesecond patterned mask comprises a second slot extending along a seconddirection and the first slot intersects the second slot to form a thirdslot; removing the second IMD layer through the third slot to form acontact hole; and forming a conductive layer in the contact hole to forma second metal interconnection for electrically connecting the firstmetal interconnection; forming a magnetic tunneling junction (MTJ) stackon the second IMD layer and the second metal interconnection; andpatterning the MTJ stack to form a MTJ on the second metalinterconnection, wherein an area of the MTJ is smaller than an area ofthe second metal interconnection.
 2. The method of claim 1, wherein thefirst patterned mask and the second patterned mask comprise differentmaterials.
 3. The method of claim 1, wherein the first patterned maskcomprises a metal mask.
 4. The method of claim 1, wherein the secondpatterned mask comprises a patterned resist.
 5. The method of claim 1,wherein the first slot comprises a rectangular slot.
 6. The method ofclaim 1, wherein the second slot comprises a rectangular slot.
 7. Themethod of claim 1, wherein the third slot comprises a square slot. 8.The method of claim 1, wherein the first direction is orthogonal to thesecond direction.